The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write magnetoresistive heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
These magnetoresistive heads typically comprise: a ferromagnetic free layer in which the magnetization angle is altered by an external magnetic field (referred to below as a free layer), and a ferromagnetic layer which is magnetically fixed in one direction by an antiferromagnetic layer and is stable with respect to external magnetic fields (referred to below as a fixed layer). Such a suitable magnetic field is usually applied using magnetic domain control films disposed on either side of the free layer, such that the initial magnetization angle of the free layer is parallel to the ABS and lies at 90° with respect to the fixed layer.
Recorded information is generally reproduced by utilizing the difference in resistance produced due to changes in the magnetization angle of the free layer and changes in the relative angle between the fixed layer and the free layer. This phenomenon is believed to be caused by the synthesized magnetic field comprising the magnetic domain control film and the leakage magnetic field produced by the medium. If the magnetic field of the magnetic domain control layer applied to the free layer is too intense, a relative angle between the fixed layer and the free layer is not readily achieved, and the output drops. On the other hand, if the field is too weak, the absolute value of asymmetry and variations increase because of the effects of the static magnetic field produced by the fixed layer, the effects of the shape anisotropy magnetic field, etc., thus causing reading errors. Furthermore, the free layer may be endowed with multiple magnetic domains, which can cause Barkhausen Noise. In other words, it is necessary to apply a suitable magnetic field to the free layer in order to properly use the magnetoresistive head.
Therefore, the ability to provide a magnetic domain control film which makes it possible to apply a more stable magnetic field to the free layer than is conventionally achieved would be very advantageous.